Herb
Slow, immense and civic — the tree Europe used to swear on.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
An oak can stand for eight hundred years and spend the first three hundred of them growing. That timescale is most of the reason for its reputation: an oak outlasts the people who name it, and communities used them as fixed points — boundary oaks, gospel oaks walked at parish bounds, courts and moots held beneath particular trees whose names survive on maps.
The classical world gave the oak to the sky gods, Zeus and Jupiter, and lightning strikes are the usual explanation, oaks being tall, wet and frequently hit. Pliny's account of druids cutting mistletoe from an oak with a golden sickle is the single most influential paragraph in British neo-pagan history, despite being second-hand, brief and possibly wrong. Nearly everything modern practice does with oaks descends from it.
Craft treats the oak as strength, endurance, oath-keeping and the long view. Acorns go into protective charms and on windowsills; a piece of oak carried is a very old and very simple English charm. The tree's own contribution is patience, which it has in quantities nobody else can match.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Pliny the Elder, Naturalis Historia (c. 77 CE)
Pliny describes Gaulish priests cutting mistletoe from an oak with a golden sickle on the sixth day of the moon. It is a single short passage, written by a Roman about a people he had not observed, and it underpins an astonishing amount of later practice.
Carried forward
Nicholas Culpeper, The Complete Herbal (1653)
"Jupiter owns the tree," Culpeper writes, which agrees for once with the classical assignment to Jupiter and Zeus. He is generally happiest when his astrology and his authorities line up, and says so.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.